This invention relates to sodium carbonate dispersions and to a method for their preparation. More particularly, this invention concerns itself with a novel method for preparing stable microdispersions of sodium carbonate particles in hexane for use as seedant materials for endo-decoy systems.
It has been proposed to use concentrated solutions of an alkali metal salt as sources of ionizable material in endo-decoy systems. Candidate materials include the hydroxides, carbonates, formates or acetates of sodium, potassium or cesium. Halide salts cannot be used. However, the use of water solutions of alkali metal salts as seedants for endo-decoy systems has been less than satisfactory. The difficulties encountered have been due to the large droplets formed by these solutions because of the high surface tension and heat of vaporization of water. To be effective, the alkali salt containing liquid has to be dispersed as droplets finer than 10.mu. under use conditions. Consequently, the following requirements must be met if the liquid system is to operate properly and effectively. The boiling point of the system (at 1 atm) should be about 40.degree. to 80.degree. C. The heat of vaporization should be less than 120 cal/gram; while the surface tension should be 20-30 dynes/cm; the viscosity less than 10 cp; and the salt concentration should be a minimum of 10 to 20 percent by weight. Some of the common organic solvents which closely meet the requirements outlined above are the aliphatic or naphthenic hydrocarbons containing five or six carbon atoms such as acetone, benzene, cyclohexane cyclopentane, diethyl ether, ethanol, methyl alcohol, n-hexane, n-pentane, and methyl pentane.
Although the above-mentioned liquids are poor solvents for inorganic salts, it has been found that alkali metal salts microdispersions that are stable in these liquids can be prepared by the method of this invention.
In brief, the method involves starting with a colloidal sodium carbonate dispersion in a non-volatile oil followed by the steps flocculation, re-dispersion, centrifugation and vacuum distillation to effect the substitution of the non-volatile oil solvent with a volatile organic solvent such as n-hexane.